Master/slave hydraulic system with rebound compensation

Abstract

A master/slave hydraulic system (10) comprises a master cylinder (12), slave cylinders (14-22), and a rebound compensator (72) for eliminating the effects of expansibility in the system on the lower stroke of the cylinders so that accurate depth control across an agricultural implement can be achieved and maintained. The rebound compensator (72) includes a direct pressure reducing and relieving valve (74) and a check valve (86). A flow restrictor (90) is preferably provided on the high-pressure supply port of the pressure reducing and relieving valve (74).

What is claimed is: 
     
       1. In a hydraulic system including a reversible control valve actuating a master cylinder fluidly connected in series with a plurality of slave cylinders, between raised and lowered positions, the improvement comprising: a direct pressure reducing and relieving valve having a high-pressure supply port fluidly connected to one side of the control valve, a reduced pressure supply port fluidly connected to the endmost slave cylinder, and a pressure relief port fluidly connected to the other side of the control valve and to the master cylinder;   a check valve fluidly connected across said direct pressure reducing and relieving valve, between said endmost slave cylinder and said one side of the control valve; and   a flow restrictor fluidly connected between said one side of the control valve and the high-pressure supply port of said direct pressure reducing and relieving valve.   
     
     
       2. A master/slave hydraulic system for precise depth control of soil-working tools on an agricultural implement, comprising: a reversible control valve having raise and lower ports;   a master cylinder having a movable rod and raise and lower ports;   a plurality of slave cylinders connected in series with said master cylinder, each slave cylinder including a movable rod and raise and lower ports;   a pressure reducing and relieving valve having a high-pressure supply port fluidly connected to the lower port of said control valve, a reduced pressure supply port fluidly connected to the lower port of the endmost slave cylinder, and a pressure relief port fluidly connected to the raise port of said master cylinder and to said control valve;   means associated with said master cylinder for limiting stroke of the rod in said master cylinder;   a check valve connected across said pressure reducing and relieving valve between the lower port of said control valve and the lower port of said endmost slave cylinder; and   a flow restrictor connected to the high-pressure supply port of said direct pressure reducing and relieving valve.   
     
     
       3. The master/slave hydraulic system of claim 2, wherein said pressure reducing and relieving valve is of the pilot-operated, adjustable spool-type. 
     
     
       4. A master/slave hydraulic system for precise depth control of soil-working tools on an agricultural implement, comprising: a reversible control valve having raise and lower ports;   a master cylinder having a movable rod, a raise port, and a lower port;   a normally open poppet valve connected between the raise port of said control valve and the raise port of said master cylinder;   an adjustable stop mounted on the rod of said master cylinder for engagement with said poppet valve in order to close fluid communication between said control valve and said master cylinder and thus limit stroke of the rod in said master cylinder;   a plurality of slave cylinders connected in series with said master cylinder, each slave cylinder including a movable rod and raise and lower ports;   a direct pressure reducing and relieving valve having a high-pressure supply port fluidly connected to the lower port of said control valve, a reduced pressure supply port fluidly connected to the lower port of the endmost slave cylinder, and a pressure relief port fluidly connected to the raise port of said control valve;   a check valve fluidly connected across said direct pressure reducing and relieving valve between the lower port of said control valve and the lower port of said endmost slave cylinder; and   a flow resistor fluidly connected between the lower port of said control valve and the high-pressure supply port of said direct pressure reducing and relieving valve.   
     
     
       5. A rebound compensator for use in a master/slave hydraulic system including a reversible control valve fluidly connected between two lines for supply and return of fluid under pressure, one line being fluidly connected to a master cylinder and the other line being fluidly connected to an endmost slave cylinder which is fluidly connected in series with at least one other slave cylinder and the master cylinder, which compensator comprises: a direct pressure reducing and relieving valve having a high-pressure supply port for fluid connection to one side of the control valve, a reduced-pressure supply port for fluid connection to the endmost slave cylinder, and a pressure relief port for fluid connection to the other side of the control valve and to the master cylinder;   a check valve fluidly connected across said direct pressure reducing and relieving valve, between said endmost slave cylinder and said one side of the control valve; and   a flow restrictor fluidly connected between said one side of the control valve and the high-pressure supply port of said direct pressure reducing and relieving valve.   
     
     
       6. The rebound compensator of claim 5, wherein said direct pressure and relieving valve is of the pilot-operated, adjustable spool-type.